The present invention relates to dispersants for use in fuels and in engine oil lubricants, especially for reducing soot-induced viscosity increase in heavy duty diesel engine lubricants.
Heavy duty diesel vehicles may use exhaust gas recirculation (EGR) engines in efforts to reduce environmental emissions. Among the consequences of recirculating the exhaust gas through the engine are different soot structures and increased viscosity of the oil at lower soot levels, compared with engines without EGR. It is desirable that oil exhibit minimal viscosity increase, e.g., less than 12 mm2/sec (cSt) at 100° C. at a soot loading of 6 weight %.
It is also desirable that a lubricating oil composition maintain a relatively stable viscosity over a wide range of temperatures. Viscosity improvers are often used to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved.
Traditional dispersant viscosity modifiers (DVMs) made from ethylene-propylene copolymers that have been radically grafted with maleic anhydride and reacted with various amines have shown desirable performance to prevent oil thickening in diesel engines. Aromatic amines are said to show good performance in this regard. DVMs of this type are disclosed in, for instance, U.S. Pat. Nos. 4,863,623, Nalesnik et al., Sep. 5, 1989; 6,107,257, Valcho et al., and 6,107,258, Esche et al., each Aug. 22, 2000, and U.S. Pat. No. 6,117,825, Liu et al., Sep. 12, 2000.
U.S. Pat. No. 5,409,623, Mishra et al., Apr. 25, 1995, discloses functionalized graft copolymers as viscosity index improvers, comprising an ethylene alpha-monoolefin copolymer grafted with an ethylenically unsaturated carboxylic acid material and derivatized with an azo-containing aromatic amine compound. U.S. Pat. No. 5,264,140, Mishra et al, Nov. 23, 1993, discloses similar polymers derivatized with an amide-containing aromatic amine material. U.S. Pat. No. 5,264,139, Mishra et al., Nov. 23, 1993, discloses similar polymers derivatized with a sulfonyl-containing aromatic amine material. U.S. Pat. No. 5,620,486, Cherpeck, Apr. 15, 1997, discloses fuel compositions containing aryl succinimides, that is, an effective detergent amount of a compound of the formula
wherein R is a hydrocarbyl group having an average molecular weight of about 400 to 5,000; and R1 and R2 are independently selected from the group consisting of hydrogen, hydroxy, —CO2H, —NO2, and —NR3R4. A fuel soluble nonvolatile carrier fluid or oil may also be used with the aryl succinimide.
The present invention, therefore, solves the problem of providing a low cost dispersant viscosity modifier having improved performance in engine tests, providing a good viscosity index and good soot dispersion and toleration properties, particularly in diesel engines, and especially in heavy duty diesel engines employing exhaust gas recirculation.